讨论一个阅读 36套里面第3套dust 的那一篇

vanessachemUID: 3100834

The dark regions in the starry night sky are not pockets in the universe that are devoid of stars as had long been thought. Rather, they are dark because
of interstellar dust that hides the stars behind it. Although its visual effect is so pronounced, dust is only a minor constituent of the material, extremely
low in density, that lies between the stars. The average density of interstellar material in the vicinity of our Sun 1,000 to 10,000 times less than the best terrestrial laboratory vacuum. It is only because of the enormous interstellar distances that so little material per unit of   volume becomes so significant. Optical astronomy is most directly affected, for although interstellar gas is perfectly transparent, the dust is not. (125 words)   

前面是在说天上的黑的地方是因为有dust把星星遮住了。 然后 dust is only a minor constituent of the material, 这是想说其实是这种material 在作用么？
然后说dust 密度低。  
因为距离很大， 所以每个unit of volume里面的东西反而变得重要？ 怎么感觉没神马逻辑呢？

下面这个为什吗不选a 要选c呢？ 请高人指点

2. It can be inferred from the passage that it is   
   because space is so vast that   
(A) little of the interstellar material in it seems substantial
(B) normal units of volume seem futile for measurements  
of density
(C) stars can be far enough from Earth to be obscured  
even by very sparsely distributed matter
(D) interstellar gases can, for all practical purposes, be   
regarded as transparent   
(E) optical astronomy would be of little use even if no  
interstellar dust existed

846136085UID: 2987171

1# vanessachem
定位在最后一句“
Optical astronomy is most directly affected, for although interstellar gas is perfectly transparent, the dust is not.”
距离远，而且那么多dust，所以看不清楚嘛，就C咯
A选项，在原文里根本没提到substantial的问题，所以不选

狮子王UID: 2976724

正因为宇宙空间距离大了，所以即使是低密度的空间物质，累积起来对视觉的效果就很明显了。

vanessachemUID: 3100834

恩 有道理